Imaging pyrometer

ABSTRACT

In the imaging pyrometer, at least three types of pixels (L, S, V) for sensing electromagnetic radiation in at least three different spectral ranges are arranged in a mosaic pattern. In a neighborhood, there are two types of pixels with relatively narrow spectral sensitivity ranges in the infrared (IR), a first one (L) for sensing longer IR wavelengths and the other one (S) for shorter IR wavelengths. Additionally, there is a third pixel type (V) present for receiving electromagnetic radiation in a broader band such as the visible part of the electromagnetic spectrum. This is preferably realized by placing a mosaic filter pattern directly on pixels of an appropriate optoelectronic image sensor, for example by evaporation and photolithographic definition. The pyrometer makes it possible to measure two images of a scene simultaneously and in perfect geometric registration: a reliable temperature map, based on the two-wavelength pyrometric measurement technique, and a high-resolution picture of the scene, for example in the visible spectral range. The dynamic range for the temperature map measurement and the simultaneous picture acquisition are be increased compared to the prior art, so that both images are acquired under favorable signal-to-noise conditions, and the measurable temperature range between about 350° C. and several 1000° C. is accessible without additional neutral density filters or aperture stops.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an imagine pyrometer and a method forsimultaneously determining surface temperature distributions and imagesof remote objects.

2. Description of Related Art

In machine vision and automatic manufacturing, high-resolutiontemperature maps and visible imagery must simultaneously be acquiredthat need to be in perfect geometric registration. In such applications,the readout speed of a complete frame or a sub-game must typically be 10Hz or faster and the temperature range should be between 350° C. andseveral 1000° C.

U.S. Pat. No. 4,413,324 (Tatsuwaki et al.) describes an imagingpyrometer that makes use of an image pickup device whose pixels arecovered with a mosaic of two types of infrared transmissive filters. Thesignals of two neighboring pixels are converted into a temperature valueas in conventional two-wavelength pyrometers. This imaging pyrometer iscapable of acquiring a two-dimensional temperature map of a scene.However, no provisions are foreseen to accommodate a large range oftemperatures, requiring an unusually large dynamic range of the filteredpixels. Additionally, the temperature map is the only pictorialinformation acquired, and no visual image of the scene can be taken, forexample in the visible spectral range, as is often required in machinevision for high-resolution optical inspection.

International publication No. WO-99/27336 (Koltunov et al.) describes anextension of U.S. Pat. No. 4,413,324 (Tatsuwaki et al.). The number ofdifferent types of infrared transmissive filter in a pixel is increasedfrom 2 to N, where N is a natural number. This makes it possible todetermine two-dimensional maps not only of the temperature but also theemissivity. As in U.S. Pat. No. 4,413,324 (Tatsuwaki et al.), noprovision is foreseen to measure anything other than the temperature andemissivity map, or to accommodate a large range of temperaturesrequiring a usually large dynamic range of the filtered pixel in thefilter mosaic.

U.S. Pat. No. 4,687,344 (Liliquist et al.) describes an imagingpyrometer that partially overcomes the limitations of Tatsuwaki et al.This device also consists of a single image pickup device, but it iscompletely covered with a single infrared transmission filter. Dependingon the temperature range of interest, additional neutral density filterscan be inserted to increase the effective dynamic range and thereforethe temperature measurement range of the imaging pyrometer. However,since only one type of infrared filter is used, no two-wavelengthcorrection can be made for surface properties of the emitting objectssuch as varying emissivity or surface finish, potentially leading toincorrect temperature readings. As in Tatsuwaki et al., only atemperature map is produced without any visible image.

U.S. Pat. No. 5,337,081 (Kamiya et al.) describes a triple-view imagingpyrometer, making use of a single image pickup device. The radiationincident from a scene is separated in two or more wavelength bands, andthe resulting images of different wavelength bands are imaged ontodifferent areas of the same single image pickup device. In this way, theregistration problem is solved that exists when several different imagepickup devices are used as described in previous patents. In this way,one can for example simultaneously acquire two-wavelength data for thecalculation of the temperature map, as well as a visible image of thescene. However, the necessary optics to achieve the wavelength bandseparation and image combination for a single image pickup device is nottrivial.

U.S. Pat. No. 5,963,311 (Craig et al.) describes an imaging pyrometerthat makes use of a single image pickup device. In similar fashion as inKamiya et al., beam splitting arid image combination optics is used toseparate two wavelength ranges in the incoming radiation and to combinethe two images onto one single image pickup device. The disclosedoptical arrangement assures that the two images are in good geometricalregistration on the image sensor. The two images are then used forconventional two-wavelength pyrometric determination of the temperaturetrap. However, the required optics is not trivial, and only atemperature map is acquired in this method.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an imaging pyrometerand a method for measuring surface temperature distributions of remoteobjects that overcome the above limitations of the prior art. Moreparticularly, the invention shall solve the following two majorproblems:

(a) Two images of a scene shall be measured simultaneously and inperfect geometric registration: a reliable temperature map, based on thetwo-wavelength pyrometric measurement technique, and a high-resolutionpicture of the scene, for example in the visible spectral range.

(b) The dynamic range for the temperature map measurement and thesimultaneous picture acquisition shall be increased compared to theprior art, so that both images are acquired tinder favorablesignal-to-noise conditions, and the measurable temperature range betweenabout 350° C. and several 1000° C. is accessible without additionalneutral density filters or aperture stops.

The basic idea of the invention is to arrange at least three types ofpixels for sensing electromagnetic radiation in at least three differentspectral ranges in a mosaic pattern. This pattern has the followingproperties. In a neighborhood, there are two types of pixels withrelatively narrow spectral sensitivity ranges in the infrared (IR), afirst one (L) for sensing longer IR wavelengths and the other one (S)for shorter IR wavelengths. Additionally, there is a third pixel type(V) present for receiving electromagnetic radiation in a spectral rangewhich is different from the sensitivity ranges of the first (L) andsecond (S) pixel types. (“Different” means in this connection that thereare wavelengths in one spectral range that are not contained in theother spectral range.) This third pixel type V has the property of beingdensely arranged and regularly spaced, so that high-resolution, finelysampled images of the scene can be measured through these pixels,without being influenced by the measurements of the IR-sensitive pixelsL, S. The sensitivity range of the third pixel type (V) is preferablyadapted to the illumination of the scene to be imaged. Preferably, it isbroader than the first (L) and second (S) sensitivity range, e.g., atleast three times broader, and typically lies within or covers thevisible part of the electromagnetic spectrum. Alternatively, it also maybe relatively narrow, e.g., for cases where the scene is illuminated bya narrow-band light source such as a light emitting diode (LED).

In a preferred embodiment of the pyrometer according to the invention, amosaic filter pattern is placed directly on pixels of an appropriateoptoelectronic image sensor, for example by evaporation andphotolithographic definition. Such color filters are well known in theart and may be, e.g., dielectric layer stacks, dye filters and/ordiffractive filters (cf. K. Knop. “Color Pictures Using the ZeroDiffraction Order of Phase Grating Structures”, Optics Communications.Vol. 18, No. 3, 298-303, 1976). The first and the second type ofIR-sensitive pixels L, S are related to two different types of IRtransmission filters, a first one transmitting longer IR wavelengths,with a maximum transmission towards the longest wavelength where theimage sensor is still sensitive, the other one at shorter IRwavelengths. The third type of pixels V can be related to a third typeof filters transmitting in the visible part of the electromagneticspectrum, or it could yield maximum sensitivity by avoiding a filterdeposition on the corresponding pixels.

As an alternative, one can also use more than one imaging, filter typeV₁ . . . V_(n), each of which has a different central wavelength andpossibly a different spectral width.

To increase the dynamic radiometric and temperature range, and to adaptthe signal levels of the differently sensitive pixels (L, S and V), theexposure times are adjusted to the actual radiation levels: if thetemperature is high, then a relatively short exposure time is requiredto bring the L and S signals to a sufficiently high level. At 1000° C.,for example, exposure times of a few hundred microseconds are sufficientfor a typical silicon-based CCD or CMOS image sensor. At 400° C.,however, exposures of several tens of milliseconds are required to reachthe same signal level. Depending on the (additional) illumination level,the optimum exposure for the V pixels might be higher or lower than theone for the L and S pixels.

Depending on the type and capabilities of the solid-state image sensoremployed, different means are available to adapt the exposure tine tothe brightness level of the radiation:

(i) In a charge-coupled device (CCD) image sensor (of frame-transfer,interline-transfer or field-interline,transfer architecture), all pixelshave the same exposure time. One can employ, therefore, two or morecomplete image acquisition cycles, each with its own exposure time. Twodifferent exposure times are required when S and L pixels show similarsignal levels and only V has a different signal level. Three exposuretimes are required when S, L and V pixels show all different signallevels. More than three exposure times are appropriate when S, L and V₁all show different signal levels, in the case of more than one Vchannel.

(ii) In a complementary-metaloxide-semiconductor (CMOS) image sensor oran active-pixel sensor (APS), it is possible to have a differentexposure time for each imager line, for each column or even for eachpixel. With such an image sensor type, it is not necessary to acquirethree different images: it is rather possible to give each pixel type(S, L or V) its optimum exposure time, depending on temperature andillumination conditions. Since CMOS or APS image sensors offernon-destructive readout, this can be accomplished, for example, byreading out pixels which need short exposure times earlier than pixelswith a long exposure time, relative to a reset signal given to thepixels.

The imaging pyrometer according to the invention has, among others, thefollowing possible applications:

Laser welding. For controlling the laser power that must be highinitially, until the surface of the object starts to become liquid andincreases its absorbance suddenly, when the laser power must be reducedwithin a few 100 μs so as not to evaporate the material but rather keepit in the liquid phase.

Laser drilling and cutting. For controlling the intensity of the laserused in drilling and cutting processes, and for advancing the object atthe optimum speed. This can be done by observing the temperature aroundthe cutting position.

Gas or electric welding. For controlling the speed at which an objectadvances under a gas or electric welding torch. The temperature is ameasure for the optimum speed with which the welding can proceed.

Hot-air fusion of plastic materials. Plastic materials can be fused(“welded”) by hot-air guns. In order not to burn the plastics, it isimportant to control the temperature of the hot air and the advancementof the materials to be welded. By observing the temperature map acrossthe width of the hot air, dangerous hot spots and potential burns can bedetected early and avoided.

Combustion process monitoring. The imaging pyrometer can observesimultaneously the burning pattern of a flame (“how it dances”) and thecombustion temperature. This information can be used to optimize thecombustion process for lower pollutant emission and higher burnerefficiency.

Combustion motor optimization. By observing at the same time the surfacetemperatures of parts in an internal combustion motor (e.g., a Dieselengine) and the precise motion of the different motor elements, thegeometry of the engine and details of the combustion process can beoptimized.

Monitoring of heat treatment. Various industrial processes call for aheat treatment that often needs to be uniform. An example is theso-called rapid thermal annealing (RTA) employed in the semiconductorindustry. Since this is realized with an array of lamps, active lampcontrol and RTA optimization with the disclosed imaging pyrometer ispossible.

Glass, metal and ceramic processing. Industrial processes that make useof the controlled melting, forming and cooling of substances (such asglass, metal or ceramics) sometimes result in products that haveinternal stress and are therefore prone to failure because the coolingprocess was not uniform and slow enough. Closed-loop control of suchmelting-forming-cooling processes is possible with the imagingpyrometer.

BRIEF DESCRIPTION OF THE DRAWINGS

These and further features of the invention will be apparent withreference to the following description and drawings, wherein:

FIGS. 1-4 show various pixel arrangements in a pyrometer according tothe invention;

FIG. 5 shows a graphical representation of the wavelength dependenciesof (a) the power radiated by a black body, (b) the spectral sensitivityof Si and (c) sensitivities of the various pixel types of the pyrometeraccording to the invention;

FIG. 6 shows a block diagram of a pyrometer according to the inventionwith an active feedback; and

FIG. 7 shows a schematic of an APS pixel circuit of a pyrometeraccording to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1-4 schematically illustrate four different types of pixelarrangements in a pyrometer according to the invention. The pyrometer isbased on an appropriate solid-state image sensor, preferably an Sisensor, comprising a plurality of pixels. There are at least threedifferent types of pixels:

Type L: sensitive at longer IR wavelengths;

Type S: sensitive at shorter IR wavelengths; and

Type V: sensitive in a further, preferably broader spectral band, e.g.,in the visible part of the electromagnetic spectrum.

The different sensitivities are preferably achieved by coating thesensitive areas of the pixels by a mosaic of appropriate filters. Thepixel arrangements are two-dimensional patterns consisting of a periodicrepetition of a unit cell. The unit cell, marked in gray in FIGS. 1-4,comprises all pixel types involved in the respective pyrometer.

FIG. 1 shows a pixel arrangement with a 1×3 unit cell (defined, e.g., bya stripe filter) and three different pixel types L, S and V. FIG. 2shows a pixel arrangement with a 1×4 unit cell (defined, e.g., by astripe filter) and three different pixel types L, S and V. FIG. 3 showsa preferred pixel arrangement with a 2×2 unit cell (defined, e.g., by amosaic filter) and three different pixel types L, S and V. It is notedthat, in the pixel arrangements illustrated in FIGS. 1-3, a surfacedensity of the third pixel type V is greater than the surface density ofthe first pixel type L and is greater than the surface density of thesecond pixel type S. FIG. 4 shows a pixel arrangement with a 2×2 unitcell (defined, e.g. by a mosaic filter) and four different pixel typesL, S, V₁ and V₂.

FIG. 5 illustrates the functioning of an Si-based pyrometer according tothe invention with three different filter types. FIG. 5(a) shows agraphical representation of the power P(,λ) radiated by a black body ata given temperature versus the wavelength λ according to Planck'sradiation law${{dP}( {\vartheta,\lambda} )} = {\frac{2{hc}^{2}}{\lambda^{5}}\frac{A}{^{{hv}/{{k\lambda}{({\vartheta - \vartheta_{n}})}}} - 1}d\quad {\lambda.}}$

where

dP(, λ) is the Power radiated in the wavelength range [λ, λ+dλ]

dλ is the wavelength-interval width,

h=6.63·10⁻³⁴ Js is Planck's constant,

c=3.00·10⁸ m/s is the velocity of light in vacuum,

k=1.38·10⁻²³ J/K is Boltzmann's constant,

₀=−273.15° C.: is the absolute-zero temperature in ° C., and

A is the area of the body.

The two curves correspond to two different temperatures ₁ (e.g., ₁=350°C.) and ₂>₁ (e.g., ₂=1000° C). FIG. 5(b) shows the spectral sensitivityη(λ) of Si, i.e., of the photosensitive detectors used in this type ofpyrometer. This curve is given by the material properties of Si; itstarts at about λ≈0.2 μm, reaches its maximum at about λ≈0.8 μm and endsat about λ≈1.2 μm. FIG. 5(c) shows transmission curves T(λ) of threeexemplified filters used in the pyrometer. A first narrow-band filter Land a second narrow-band filter S transmit, at central wavelengthsλ_(L)≈1.06 μm and λ_(s)≈0.99 μm, respectively, and have spectral widthsof about Δλ≈0.07 μm. A third bandpass filter V transmits, e.g., in theentire visible range. i.e., for wavelengths λ_(L) between 0.39 and 0.77μm; its spectral width of Δλ=0.38 μm is thus about five times largerthan that of the first and second filters L, S. The output signal ofeach pixel type L, S, V for a given temperature is essentially theintegral of the product of the functions P(,λ), η(λ) and T(A) integratedover the entire spectrum (0<λ<∞).

Because transmission bands of the filters L and S are very narrow, thepixels L and S essentially measure the radiated powers P(,λ) andP(,λ_(s)), respectively. From their output signals, processed bysuitable electronics, a microprocessor or a computer, the temperature iscalculated according to a known two-wavelengths-pyrometer algorithm (cf.U.S. Pat. No. 4,413,324 by M. Tatsuwaki et al., “Temperature PatternMeasuring Method and a Device Therefore”, col. 6. line 40 ff). In anexemplified algorithm, the ratio l/s of a longer-wavelength filteredpixel value l divided by a shorter-wavelength filtered pixel value s iscalculated, and the ratio l/s is fed into a lookup table whose output isthe temperature. The contents of this lookup table can be calculatedbased on Planck's radiation law, the knowledge of the twonear-infrared-filter characteristics T_(L)(λ) and T_(s)(λ), and thesensor sensitivity η(λ). The high-resolution visual image is determinedby interpolation between the sampled outputs of the pixels V in theimage. This sampling occurs according to known interpolation algorithmssuch as bilinear interpolation (cf. Th. Pavlidis. “Algorithms forGraphics and Image Processing”, Computer Science Press, 1982, Sec. 10.2“Polynomial Interpolation”).

FIG. 6 shows a block diagram of a pyrometer according to the inventionwith an active feedback. An image sensor 1 (shown schematically, withonly 3×3 pixels) of the CMOS active pixel sensor (APS) type is read outpixel by pixel by applying a row address 8 and a column address 9 toaddress decoder circuits 2 and 3, respectively. The output signals ofthe pixels are read out by a buffering circuit 4, and the signals arestored and processed in a pre-processing circuit 5. The pre-processingcircuit 5 is responsible for calculating a temperature map (x,y) and avisual image l(x,y), where x and y are the coordinates of the sensorplane.

The temperature map (x,y) and the intensity image l(x,y) are fed into aprocessing unit 6 which calculates results and outputs them using one ormore channels 7.1, 7.2 of information. This processing unit 6 calculatessuch information as what is the distribution of the temperature map(x,y) to determine non-uniform patterns of potential overheating,development of the high-temperature zone and direction of a potentialmotion of the high-temperature zone. This information can be used, forexample, to regulate the power of a laser used for drilling, cutting orwelding, or the optimum path for a welding torch. Based on the sameinformation, it is also possible to determine where interestingsub-images (so called “regions of interest”, ROIs) are in the imagesensor. The information about interesting ROIs is used to generatesequences of row addresses 8 and column addresses 9, which are used toread out the next ROls in the image sensor.

In FIG. 7, a schematic of a CMOS APS pixel circuit of a pyrometeraccording to the invention is shown. A CMOS APS circuit consists in itssimplest form of a photodiode 11 in which a photocurrent produced byincident electromagnetic radiation 10discharges the space charge regionof the photodiode 11. The resulting voltage is sensed using a sourcefollower transistor 12 connected by a column bus 14 to a load transistor(not shown), which is common for all pixels in, a column. The selectionof an individual pixel is realized with a row select transistor 13,which connects a particular source follower transistor 12 with thecolumn bus 14. Since the photodiode 11 is discharged by thephotocurrent, it must be periodically recharged to a reference voltageVDD by a so-called reset transistor 15.

Compared to CCD pixels, the CMOS APS pixel shown in FIG. 7 has the bigadvantage that each pixel can be accessed individually, and it can alsobe reset individually. This is the key property used forillumination-dependent (active) exposure control: depending on thephotocurrent in the photodiode 11, the timing of the reset transistor 15is adapted so as to produce a signal voltage at the source followertransistor 12 that is neither over-saturated nor hidden in the noise. Inaddition to exposure, other parameters of the pyrometer may be varied byuser input or automatically, such as the readout window, the readoutspeed or the dynamic range.

By reading out only a selected area (“region of interest”, ROl) of theimage sensor, the readout speed and the achieved frame rates aresignificantly increased. A ROl can be a small area, or it can be aone-dimensional curve such as a circle.

The pyrometer image sensor can be sub-sampled to increase readout speedand frame rate. This is achieved by periodically skipping the readout ofseveral of the unit cells illustrated in FIGS. 1-4. In this way, thewhole field of view can be sampled for intensity and temperature maps,albeit less densely.

The dynamic range of each pixel can be increased if each pixel is readout twice: once with a short exposure tinge t_(short), and once with along exposure time t_(long), By adding the second value to the productof the first value multiplied with the ratio (t_(long)/t_(short)), apixel value with larger dynamic range is obtained.

Numerous other embodiments may be envisaged, without departing from thespirit and scope of the invention.

What is claimed is:
 1. A method for simultaneously determining surfacetemperature distributions (x,y)) and images of remote objects,comprising the steps of: generating one single image of said objects,sensing said image essentially simultaneously in a first infraredspectral range, in a second infrared spectral range, which is differentfrom said first infrared spectral range, and in at least one furtherspectral range, which is different from said first and second infraredspectral ranges, and determining a surface the temperature distribution((x,y)) from said images sensed in said first and second infraredspectral ranges, wherein a visual image (l(x,y)) is determined from saidimage or images sensed in said at least one further spectral rangewithout being influenced by images sensed in said first and secondinfrared spectral ranges.
 2. The method according to claim 1, whereinsaid at least one further spectral range lies within or comprises avisible part of the electromagnetic spectrum.
 3. The method according toclaim 3, wherein at least two images are sensed in two successivereadouts and an exposure, a readout window, a readout speed and/or adynamic range are varied from one readout to the other.
 4. The methodaccording to claim 1, wherein the objects are illuminated by light withwavelengths that are at least partially contained in said at least onefurther spectral range.
 5. The method according to claim 1, wherein saidimage is sensed by an optoelectronic sensor (1) with a plurality ofpixels, each pixel sensing with an exposure time, and the exposure timesare chosen in dependence upon a radiation level of said image.
 6. Themethod according to claim 5, wherein for at least two different pixelsthe exposure times for sensing are set individually.
 7. The methodaccording to claim 6, wherein said pixels are arranged in rows andcolumns and for each row, each column or each pixel the exposure timesare set individually.
 8. Use of the method according to claim 1, inlaser welding, laser drilling or cutting, gas or electric welding,hot-air fusion of plastic materials, combustion process monitoring,combustion motor optimization, monitoring of heat treatment or in glass,metal or ceramic processing.
 9. An imaging pyrometer for simultaneouslydetermining surface temperature distributions ((x,y)) and images ofremote objects, comprising: an optoelectronic sensor (1) with aplurality of pixels of at least three different types (L, S, V) forsensing electromagnetic radiation whereof a first pixel type (L) isdesigned for sensing in a first infrared spectral range a second pixeltype (S) is designed for sensing in a second infrared spectral range,which is different from said first infrared spectral range, and, atleast one further pixel type (V) is designed for sensing in at least afurther spectral range, which is different from said first and saidsecond infrared spectral range, means (5) for determining a temperaturedistribution ((x,y)) from output signals of pixels of said first (L) andsecond (S) type, wherein the imaging pyrometer comprises means (5) fordetermining a visual image (l(x,y)) from output signals of pixels ofsaid at least one further pixel type (V) without being influenced by theoutput signals of the pixels of said first (L) and second (S) pixeltypes, and the first, second and at least one further pixel types (L, S,V) are arranged in a mosaic pattern on said optoelectronic sensor. 10.The imaging pyrometer according to claim 9, wherein said at least onefurther pixel type (V) is senses a visible part of the electromagneticspectrum.
 11. The imaging pyrometer according to claim 9, wherein asurface density of said at least one further pixel type (V) is largerthan a surface density of said first pixel type (L) and larger than asurface density of said second pixel type (S).
 12. The imaging pyrometeraccording to claim 9, wherein at least two of said first, second, and atleast one further pixel type (L,S,V), comprise filters forelectromagnetic radiation, said filters being selected from the groupconsisting of dielectric layer stacks, dye filters, and diffractivefilters.
 13. The imaging pyrometer according to claim 12, wherein saidfirst pixel type (L) comprises a first narrow-band transmission filterhaving a central wavelength (λ_(L))of 1.06 μm and a spectral width ofabout 0.07 μm, and said second pixel type (S) comprises a secondnarrow-band transmission filter having a central wavelength (λs) of 0.99μm and a spectral width of about 0.07 μm.
 14. The imaging pyrometeraccording to claim 9, wherein said mosaic pattern consists of a periodicrepetition of a unit cell, which comprises all pixel types (L, S, V)involved in the pyrometer.
 15. The imaging pyrometer according to claim14, wherein said unit cell is a square of 2×2 pixels, two diagonallyarranged pixels of the unit cell being of said first pixel type (L) andof said second pixel type (S), respectively, and the other two pixelsbeing of said at least one further pixel type (V, V₁, V₂).
 16. Theimaging pyrometer according to claim 9, wherein said optoelectronicsensor is a solid-state image sensor of technology selected from thegroup consisting of: CCD, CMOS, and APS.
 17. The imaging pyrometeraccording to claim 16, wherein said optoelectronic sensor is a CMOS APSsensor comprising a pixel with a photodiode (11), said photodiode (11)being connected to a source follower transistor (12) and, via a resettransistor (15), to a reference voltage (V_(DD)), and wherein saidfollower transistor (12) is connected to a load transistor via a rowselect transistor (13).
 18. The imaging pyrometer according to claim 9,wherein each pixel senses impinging radiation during an exposure time,and the imaging pyrometer additionally comprises means (15) for settingthe exposure times of said pixels in dependence of a radiation levelimpinging on said pixels.
 19. The imaging pyrometer according to claim18, comprising means (15) for individually setting the exposure timesfor at least two different pixels.
 20. The imaging pyrometer accordingto claim 19, wherein said pixels are arranged in rows and columns andthe imaging pyrometer comprises means (15) for individually setting theexposure times for each row, each column or each pixel.
 21. Use of theimaging pyrometer according to claim 9 in laser welding, laser drillingor cutting, gas or electric welding, hot-air fusion of plasticmaterials, combustion process monitoring, combustion motor optimization,monitoring of heat treatment or in glass, metal or ceramic processing.